Vacuum casting process

ABSTRACT

The disclosure relates to a process and apparatus for casting metals by controlling the relative pressure of the space above the molten metal body to be cast with respect to the pressure within the interior of the mold. Numerous features of the mechanism are shown and described.

I United States Patent [151 3,677,332 Smiernow [451 July 18, 1972 s41VACUUM CASTING PROCESS 3,435,878 4/l969 Howard et al. ...164/51 2 871533 2/1959 Swainson 164/1 33 [72] Inventor: George A. Smlemow, 825 S.48th Street,

Philadelphia, Pa. [9143 3,523,785 8/1970 Gero 164/ l 33 X [22] Wed: June13 1969 FOREIGN PATENTS OR APPLICATIONS [2 1 App]. No: 32 89 902,495l2/l944 France 164/133 Primary Examiner-J. Spencer Overholser [52] US.Cl. ..l64/l33, 266/42, 266/34 V, Assistant ExaminerV. K. Rising l64/62,164/63, 164/65 Arrorney-Jacksom Jackson and Chovanes 5 1] Int. Cl...B22d 35/00, 822d 37/00 [58] FieldofSearch ..164/62,6l,65,155,133,63;[57] ABSTRACT The disclosure relates to a process and apparatus forcasting metals by controlling the relative pressure of the space above[56] "Mamas and the molten metal body to be cast with respect to thepressure UNITED STATES NT within the interior of the mold. Numerousfeatures of the mechanism are shown and described. 3,099,053 7/l963 Ehot..164/64 3,125,440 3/1964 Homak et al ..75/49 2Clflna,4l)rawlngflgures 79 7a 7 7 a: "t 8a a! v ll "10"! "1.01:, a a, I 1 l1 //W7 /W A" 82 Q I m$1, 54 a! \a H J a 7/ g 1% m g '4 .2- a f Qg '2; 9; /02 /2# PatentedJuly 18, 1972 4 Sheets-Sheet l INVENTOR. 650190: 6 M/ER -aw PatentedJuly 18, 1972 4 Sheets$heet Patented July 18, 1972 4 Sheets-Sheet 4VACUUM cssrnvc rnocsss DISCLOSURE OF INVENTION This invention relates tothe manufacture of castings by a vacuum pouring process, andparticularly to a vacuum pouring apparatus suitable for pouring allferrous, non-ferrous and special alloy castings and ingots of differentdesign, weight and size in all kinds of molds: sand, semi-permanent,permanent, etc.

It is the main purpose of the invention to provide a new process ofvacuum pouring for the manufacture of very sound castings and ingots ofimproved quality, without blow-holes, flaws, or any other defects. WhenI refer to castings and ingots here I mean to include finished orsemi-finished metal products which may be in different operations bereferred to as ingots, blooms, billets, slabs, wirebars and castings.The invention aims to provide a single apparatus for vacuum pouring,which is simple in construction and design, and which assures arelatively economical method of manufacturing sound castings and ingotsof improved quality.

Another object is to provide a process and apparatus for vacuum pouringwhich improves the filling of the molds and permits the molds to befilled quickly, with little cooling of the liquid metal; thereby makingit possible to manufacture very thin section castings, particularly fromhigh viscosity alloys.

Another object is to provide a vacuum pouring process and device thatpermits the manufacture of castings with improved surface and higherdimensional accuracy. This is achieved through the vacuum during pouringand crystallization, and also due to the possibility of using lowpermeability molds, hard rammed from very fine-grained sands, or ofusing permanent and semi-permanent molds, which cannot be used in commonpouring methods.

Another object is to provide a vacuum pouring process and device thatpermits the manufacture of castings and ingots with improved mechanicalproperties, due to crystallization in vacuum and/or under pressure.

Another object is to provide a vacuum pouring process and device thatpermits the manufacture of castings and ingots with a decreased weightof heads and risers, or without them, thus increasing the yield ofcastings and ingots from the liquid metal, reducing the cutting off andcleaning costs.

A further object is to provide a vacuum pouring process and device thatpermits the manufacture of castings and ingots from highly oxidizablealloys, due to vacuum and/or neutral atmosphere in the mold whichprevents the liquid metal from coming in contact with the air. A stillfurther object is to provide a relatively economical vacuum pouringprocess and device for the manufacture of castings from very hightemperature melting alloys, which can be done due to rapid filling ofmolds with little cooling of the liquid metal.

Other objects and advantages of the invention will become apparent fromthe following detailed description of the apparatus. This description ismade in connection with the accompanying drawings in which the sameparts throughout the views are indicated by the same numerals as givenin the description.

The drawings show vacuum pouring mechanism for practicing the invention.

FIG. 1 is a diagrammatic partially broken plan view of the device of theinvention.

FIG. 2 is a diagrammatic partially broken axial section of the mechanismof FIG. I, showing the insertion ofa mold into the lower chamber.

FIG. 3 is a view similar to FIG. 1 showing the lower chamber closed andmetal being poured into the mold.

FIG. 4 is an enlarged fragmentary vertical section of the metal ladleand pouring nozzle, along with the upper chamber.

The lower reduced pressure chamber 16 represents a steel casting withtwo raising and lowering doors, in-door 22 and out-door 23. At thebottom of the chamber 16 is a vertical hydraulic cylinder 45 which ishermetically sealed with rubber gasket 46. Cylinder 45, whose piston 49enters chamber 16, is

fed through pipe line I30. To piston 49, a roller table 53 is fixed bymeans of leveling springs 51. Chamber I6 is mounted on beams 9. At thetop of the lower reduced pressure chamber 16, upper vacuum chamber 17 isfixed hermetically through rubber seal 73 by bolts 72.

The inside wall of the chamber 17 is protected from radiating heat by arefractory helical pipe coil 91, through which passes cooling water. Lid76 of upper chamber l7 has double walls with space 75 between the wallsfor circulation of cooling water. Lid 76 has a quartz glass window 79for the visual control of the liquid metal 98. Lid 76 swings on hinge 80and can be hermetically closed through rubber seal 82 by bolts 83.

The bottom of upper chamber 17 is formed by refractory cushion lll onwhich a refractory pouring basin or ladle 97 is placed. The basin 97 issurrounded by helical inductor coil 102 of copper tubing, insulatedbetween turns, through which water is passed for cooling the copper. Ifnecessary, high frequency alternating current may be applied to theterminals of the helix, inducing current in the liquid metal 98 andmaintaining the metal at the desired pouring temperature. The highfrequency current is supplied by a special high frequency generator, notshown on the figures.

The bottom and walls of basin 97 are formed by rammed refractorymaterials. A pouring channel 118 on the bottom of the basin, in cushion111, is formed by heavy duty high refractory tubing I13 having embeddedin it a helical coil 114 of copper tubing, insulated between turns,through which water is passed for cooling. Under the pouring channel 118in the ceiling of chamber 16 is placed a refractory ring 119, throughwhich the liquid metal from basin 97, through channel 118, is pouredinto the mold 70.

Assembled molds in flasks 65 on bottom boards 66 reach the vacuumpressure pouring station by a roller conveyor 1 to the roller turntable4. When the mold is on table 4, the table is turned to the positionshown in FIG. 1. The in-door 22, sliding on rails 27, is raised by cable29 driven by means of motor 34, reducer 35, and drum 3], all of whichare mounted on structure 32. The mold is pushed on the roller table 53into chamber 16 by means of the piston rod ll, supported by piston rodguides 12, from the pneumatic cylinder 10. Then the mold, pushedsimultaneously by piston rod ll and by the piston 41 from an auxiliaryhorizontal hydraulic cylinder 40, fed from pipe line 43, is fixed inchamber 16 by four flask guiding pins 67 in such a manner that a pouringgate 68 is placed just in front under the pouring ring 69. Then theindoor 22 is closed and by means of piston 49 and vertical hydrauliccylinder 45, the mold is raised and pressed to the ceiling of chamber16. The leveling springs 5| assure tight contact between the top surfaceof the mold and the ceiling of chamber 16. Then a reduced pressure iscreated in chamber 16 by vacuum pump 55, through tank 57 and pipe line58. This reduced pressure is controlled by gage 60 and valve 59.

A vacuum pump is connected to vacuum chamber l7 through the high vacuumgas pipe line 89a and three-way valve 90. When reduced pressure inchamber 16 and vacuum in chamber 17 are created, pouring can start.

It will be evident that in the preferred embodiment of the invention thevacuum in the upper chamber 17 either will be of a high or reasonableorder of magnitude, for example in the range between 10" and I00millimeters of mercury and preferably between 10' and l millimeter ofmercury, often controlled by the desired degassing pressure for theparticular metal. The reduced pressure in the lower chamber [6 and hencein the mold at the time of pouring, since the mold derives its pressurefrom the lower chamber, will be considerably higher than the pressure inthe upper chamber, at least l.5 times, and thus will serve to oppose theforce of gravity in causing metal to flow into the mold, causing agradual filling of the mold, free from spatter, avoiding gas cavities,and allowing for a controlled flow rate. It will be understood thatdepending on the character of the metal or alloy being poured. higher orlower pressure will be used in the chamber 16 and in the mold, but ingeneral for best results the reduced pressure in the chamber 16 shouldbe in the order of 2 millimeters of mercury to approximately oneatmosphere.

It also will be evident that in some cases it may be desirable to varythe pressure in chamber 16 and in the mold during pouring in order tocontrol the flow rate.

It will be evident that the residual gas in the chambers 16 and I? neednot necessarily be air, but residual gases which will be inert to theparticular metal or alloy may be used, for example, depending on thecomposition of the metal, inert gases such as helium or argon, orrelatively inert gases such as nitrogen. Reducing gases such as carbonmonoxide or hydrogen may be used. Naturally, in certain cases as wherethe metal has abnormal solubility for a particular gas, such gas may beavoided.

Pouring is controlled electrically by a high frequency cur rent whichflows through helical coil 114 and by the amount of cooling water whichpasses through the same pipe coil. Before the electric current isapplied, cold water passes through the helical pipe coil 1 l4 and themetal in channel 118 is solidified, thereby stopping pouring. Bydecreasing the amount of cool ing water and applying high frequencyelectric current to the terminals of the coil 4, current is induced inthe solidified metal in channel 118. These induced currents cause rapidheating and melting of metal in channel 118 and filling of mold '70. Thefilling of the mold 70 with liquid metal 98 is done in a preciselycontrolled way due to maintaining of programmed difference in vacuum inchamber 17 and reduced pressure in the mold from chamber 16. When theelectric high frequency current is cut off from coil "4, the amount ofcooling water passing through pipe "4 is increased, which solidifies themetal in channel U8 and stops pouring. After the sprue and casting aresolidified, the vacuum pumps are stopped, pressure in chamber 16 becomesatmospheric and the in and out doors 22 and 23 are raised. By loweringpiston 49, roller table 53 is also lowered to the level of rollerconveyor 120. Pushed by pneumatic piston rod ll, the mold comes out fromchamber 16 on the lead-away roller conveyor to a shake-out station. Thenthe cycle may be repeated with the next mold.

Other constructions of pouring basins or ladies can be used, forexample, a bottom pouring basin with stopper which is opened and closedby means of an electrical solenoid, as well known in the art.

It will be evident that where desired the mold may be preheated to anydesired temperature.

It will further be evident that while the invention may find its widestapplication in the casting of relatively common metals and alloys. suchas steel, stainless steel, heat resisting alloys, copper base alloys,aluminum base alloys, magnesium base alloys, nickel base alloys,chromium base alloys, and the like, it is also applicable to the castingof metals and alloys less commonly encountered and particularly thosewhich are highly reactive, as for example titanium, zirconium and niobi-The principles of the present invention may be utilized in differentways, numerous modifications and alterations, substitution of parts andchanges in construction being contemplated; it being understood that theprocess and apparatus shown in the drawings and described above and theparticular methods set forth are given merely for purposes ofexplanation and illustration, without intending to limit the scope ofthe claims to the specific details disclosed.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent is:

l. A process of casting molten metals, using a ladle or the like havinga pouring nozzle in the lower part thereof and a mold having an entranceopening or gate, which comprises applying the pouring nozzle of theladle in line with the entrance opening of the mold, artificiallycooling the molten metal within the pouring nozzle to initially blockthe pouring nozzle by solidified molten metal, maintaining a firstpressure on the molten metal in the ladle, retaining a higher pressurein the mold, then melting the metal in the pouring nozzle so that themolten metal flow can begin Into the mold and controlling the flow ofmolten metal to the mold by the relative difference in pressures betweenthe pressure in the ladle and the pressure in the mold.

2. A process of casting molten metal from a ladle or the like having apouring nozzle at a lower position, into a mold having an inlet openingor gate, which comprises bringing the inlet opening of the mold intoline with the pouring nozzle of the ladle, artificially cooling themolten metal in the pouring nozzle to cause it to solidify and initiallyblock the pouring nozzle by solidified molten metal, maintaining avacuum above the molten metal in the ladle in the range from 10' to lOOmillimeters of mercury, maintaining a pressure within the mold in therange of between 2 millimeters of mercury and about one atmosphere andat least l.5 times the absolute vacuum pressure on the upper surface ofthe molten metal within the ladle, then melting the metal within thepouring nozzle so that molten metal can begin to flow into the mold, andcontrolling the flow of molten metal to the mold by the relativedifi'erence in pressures between the pressure above the molten metal inthe ladle and the pressure in the mold.

1. A process of casting molten metals, using a ladle or the like havinga pouring nozzle in the lower part thereof and a mold having an entranceopening or gate, which comprises applying the pouring nozzle of theladle in line with the entrance opening of the mold, artificiallycooling the molten metal within the pouring nozzle to initially blockthe pouring nozzle by solidified molten metal, maintaining a firstpressure on the molten metal in the ladle, retaining a higher pressurein the mold, then melting the metal in the pouring nozzle so that themolten metal flow can begin into the mold and controlling the flow ofmolten metal to the mold by the relative difference in pressures betweenthe pressure in the ladle and the pressure in the mold.
 2. A process ofcasting molten metal from a ladle or the like having a pouring nozzle ata lower position, into a mold having an inlet opening or gate, whichcomprises bringing the inlet opening of the mold into line with thepouring nozzle of the ladle, artificially cooling the molten metal inthe pouring nozzle to cause it to solidify and initially block thepouring nozzle by solidified molten metal, maintaining a vacuum abovethe molten metal in the ladle in the range from 10 6 to 100 millimetersof mercury, maintaining a pressure within the mold in the range ofbetween 2 millimeters of mercury and about one atmosphere and at least1.5 times the absolute vacuum pressure on the upper surface of themolten metal within the ladle, then melting the metal within the pouringnozzle so that molten metal can begin to flow into the mold, andcontrolling the flow of molten metal to the mold by the relativedifference in pressures between the pressure above the molten metal inthe ladle and the pressure in the mold.